diff --git a/swift/common/utils.py b/swift/common/utils.py
index 0b5bb1eea3..6f0224c221 100644
--- a/swift/common/utils.py
+++ b/swift/common/utils.py
@@ -72,6 +72,7 @@ if not six.PY2:
     utf16_decoder = codecs.getdecoder('utf-16')
     utf16_encoder = codecs.getencoder('utf-16')
 from six.moves import cPickle as pickle
+from six.moves import configparser
 from six.moves.configparser import (ConfigParser, NoSectionError,
                                     NoOptionError, RawConfigParser)
 from six.moves import range, http_client
@@ -2965,6 +2966,17 @@ def read_conf_dir(parser, conf_dir):
     return parser.read(sorted(conf_files))
 
 
+if six.PY2:
+    NicerInterpolation = None  # just don't cause ImportErrors over in wsgi.py
+else:
+    class NicerInterpolation(configparser.BasicInterpolation):
+        def before_get(self, parser, section, option, value, defaults):
+            if '%(' not in value:
+                return value
+            return super(NicerInterpolation, self).before_get(
+                parser, section, option, value, defaults)
+
+
 def readconf(conf_path, section_name=None, log_name=None, defaults=None,
              raw=False):
     """
@@ -2986,7 +2998,19 @@ def readconf(conf_path, section_name=None, log_name=None, defaults=None,
     if raw:
         c = RawConfigParser(defaults)
     else:
-        c = ConfigParser(defaults)
+        if six.PY2:
+            c = ConfigParser(defaults)
+        else:
+            # In general, we haven't really thought much about interpolation
+            # in configs. Python's default ConfigParser has always supported
+            # it, though, so *we* got it "for free". Unfortunatley, since we
+            # "supported" interpolation, we have to assume there are
+            # deployments in the wild that use it, and try not to break them.
+            # So, do what we can to mimic the py2 behavior of passing through
+            # values like "1%" (which we want to support for
+            # fallocate_reserve).
+            c = ConfigParser(defaults, interpolation=NicerInterpolation())
+
     if hasattr(conf_path, 'readline'):
         if hasattr(conf_path, 'seek'):
             conf_path.seek(0)
diff --git a/swift/common/wsgi.py b/swift/common/wsgi.py
index 7d4246689d..1b2b86557a 100644
--- a/swift/common/wsgi.py
+++ b/swift/common/wsgi.py
@@ -32,7 +32,6 @@ from eventlet.green import socket, ssl, os as green_os
 import six
 from six import BytesIO
 from six import StringIO
-from six.moves import configparser
 
 from swift.common import utils, constraints
 from swift.common.storage_policy import BindPortsCache
@@ -41,7 +40,7 @@ from swift.common.swob import Request, wsgi_quote, wsgi_unquote, \
 from swift.common.utils import capture_stdio, disable_fallocate, \
     drop_privileges, get_logger, NullLogger, config_true_value, \
     validate_configuration, get_hub, config_auto_int_value, \
-    reiterate
+    reiterate, NicerInterpolation
 
 SIGNUM_TO_NAME = {getattr(signal, n): n for n in dir(signal)
                   if n.startswith('SIG') and '_' not in n}
@@ -56,23 +55,6 @@ except (ImportError, NotImplementedError):
     CPU_COUNT = 1
 
 
-if not six.PY2:
-    # In general, we haven't really thought much about interpolation in
-    # configs. Python's default ConfigParser has always supported it, though,
-    # so *we* got it "for free". Unfortunatley, since we "supported"
-    # interpolation, we have to assume there are deployments in the wild that
-    # use it, and try not to break them. So, do what we can to mimic the py2
-    # behavior of passing through values like "1%" (which we want to support
-    # for fallocate_reserve).
-    class NicerInterpolation(configparser.BasicInterpolation):
-        def before_get(self, parser, section, option, value, defaults):
-            if '%(' not in value:
-                return value
-            return super(NicerInterpolation, self).before_get(
-                parser, section, option, value, defaults)
-    configparser.ConfigParser._DEFAULT_INTERPOLATION = NicerInterpolation()
-
-
 class NamedConfigLoader(loadwsgi.ConfigLoader):
     """
     Patch paste.deploy's ConfigLoader so each context object will know what
@@ -80,6 +62,8 @@ class NamedConfigLoader(loadwsgi.ConfigLoader):
     """
 
     def get_context(self, object_type, name=None, global_conf=None):
+        if not six.PY2:
+            self.parser._interpolation = NicerInterpolation()
         context = super(NamedConfigLoader, self).get_context(
             object_type, name=name, global_conf=global_conf)
         context.name = name